An agricultural harvester known as a “combine” is historically termed such because it combines multiple harvesting functions with a single harvesting unit, such as picking, threshing, separating and cleaning. A combine includes a header which removes the crop from a field, and a feeder housing which transports the crop matter into a threshing rotor. The threshing rotor rotates within a perforated housing, which may be in the form of adjustable concaves and performs a threshing operation on the crop to remove the grain. Once the grain is threshed it falls through perforations in the concaves onto a grain pan. From the grain pan the grain is cleaned using a cleaning system, and is then transported to a grain tank onboard the combine. A cleaning fan blows air through the sieves to discharge chaff and other debris toward the rear of the combine. Non-grain crop material such as straw from the threshing section proceeds through a residue system, which may utilize a straw chopper to process the non-grain material and direct it out the rear of the combine. When the grain tank becomes full, the combine is positioned adjacent a vehicle into which the grain is to be unloaded, such as a semi-trailer, gravity box, straight truck, or the like; and an unloading system on the combine is actuated to transfer the grain into the vehicle.
During the process of harvesting in a combine, the desired grain is gathered and saved while crop material other than the desired grain is expelled from the combine. The crop material that contains the grain is directed to the cleaning system that has a series of sieves to separate the grain from crop residue. The grain falls through the sieve while part of the crop reside is retained by the sieve and the residue is moved across the sieve to a point of discharge. The light-weight non-crop material, referred to as chaff, is separated from the grain by the air coming from the cleaning fan across or through the sieve.
Sieves operate more efficiently if the crop material is evenly distributed across the sieves and not concentrated in a narrow area. As the combine transits a field the movement of the combine and the tilt of the ground can cause the crop material on the sieve to migrate to one location which may compromise the functioning of the sieve. To compensate for this problem many combines employ a system to level the sieves. Still further combines often have sieve sections with dividers between the sections. As the combine travels on a hill, the down hill section of a sieve section, which is leveled by a pivoting system, receives a higher volume of crop material than the uphill portion. This results in some of the grain and crop material to walk out onto the dividers.
What is needed in the art is a sieve pivoting system that reduces the propensity of the grain/crop material to be poorly distributed across the sieve sections when the combine is traversing sloped ground.